Fall 2005, Final Exam - PHY 131 FINAL EXAM, FALL 2005 Name_...

Name___________________________________ ASU ID _______________________ Signature________________________________ Recitation Section Time____________________ Recitation Instructor ________________ VERY SHORT ANSWER. Write the word or phrase that best completes each statement or answers the question. [Each question is worth 3 points.] 1) By how much are the electric and magnetic fields out of phase in an electromagnetic wave? 2) Two long, parallel wires carry identical currents in the opposite direction. If the wires are 2 cm apart, what will be the magnitude of the magnetic field far from either end and halfway between the wires? At a point 1 cm from the center of each wire, each wire generates a magnetic field of strength B. 3) A microwave oven operates at 2.4 GHz. What is the distance between wave crests in the oven? 4) Light is passed through three polarizing filters. Two have identical transmission axes while the transmission axis of the other is oriented at 45° to the others. In order to maximize the reduction of the intensity, or minimize the intensity, of the beam, in what order should the filters be placed? Write your answer in the space provided. SHOW YOUR WORK. [Each question is worth 8 points.] 5) During its 1989 encounter with Neptune, the Voyager II spacecraft was 4.5 × 10 9 km from Earth. Its images of Neptune were broadcast by a radio transmitter with a mere 21-W average power output. What would be the average intensity received at Earth if the transmitter broadcast equally in all directions? (The received signal was actually somewhat stronger because Voyager used a directional antenna.)

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